Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway of a target vessel. Stents are often used in the treatment of atherosclerotic stenosis and/or restenosis in blood vessels. “Stenosis” refers to a narrowing or constriction of the diameter of a bodily passage or orifice. Typically, stents are capable of being compressed, so that they can be inserted through small cavities via catheters, and then expanded to a larger diameter once they reach their target vessel. Mechanical intervention via stents has reduced the rate of restenosis; restenosis, however, is still a significant clinical problem. “Restenosis” refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty or valvuloplasty) with apparent success. Accordingly, stents have been modified to perform not only as a mechanical scaffolding, but also to provide biological therapy.
Biological therapy can be achieved by medicating a stent, typically referred to as a drug delivery stent. Drug delivery stents provide for the local administration of a therapeutic substance at the diseased site. In contrast, systemic administration of a therapeutic substance may cause adverse or toxic side effects for the patient because large doses are needed in order for the therapeutic substance to have an efficacious effect at the diseased site. Thus, local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery therefore produces fewer side effects and achieves more favorable results.
Stents may be made of biostable materials that remain at an implant site permanently. However, the clinical need for a stent at an implant site may be temporary. Once treatment is complete, which may include structural tissue support and/or drug delivery, it may be desirable for the stent to be removed or disappear from the treatment location. One way of having a stent disappear may be by fabricating a stent in whole or in part from materials that erode or disintegrate through exposure to conditions within the body. Stents fabricated from bioresorbable, biodegradable, bioabsorbable, and/or bioerodable materials such as bioresorbable polymers can be designed to completely erode only after the clinical need for them has ended.
A typical method for medicating an implantable device includes, for example, applying a composition containing a polymer, a solvent, and a therapeutic substance to the implantable device using conventional techniques, such as spray-coating or dip-coating. The method further includes removing the solvent, leaving on the implantable device surface a coating of the polymer with the therapeutic substance impregnated in the polymer.
In a typical spray-coating method, a stent is mounted on a mandrel of a spray-coating device. Generally, the stent will rest on, or contact components of, a mandrel (or the mandrel itself) which supports the stent and allows it to rotate during a spray-coating process. The contact between the portions of the mandrel and stent, however, inevitably cause coating defects. These defects can include cob-webbing, tearing, bridging, clumping and/or lack of coating on portions of the stent. The embodiments of the present invention are intended to address coating defect issues caused by conventional mandrel designs.
Another issue with conventional stent coating operations is one of efficiency and cost. Stent coating is typically performed one stent or scaffold at a time. For each stent coated, the coating equipment must be set up. In addition, each stent or scaffold must be loaded prior to coating and unloaded after coating. Thus, machine utilization is limited by coating only one stent for machine set-up, loading, and unloading processes.